Might not be close enough for you, but I can highly recommend Sing and Sign classes with Joanna (http://www.singandsign.com). We went to her wimbledon park classes (you can park your car in the park) but she also did classes at 'it's a kids thing' which is next to earlsfield train station, so just one stop from clapham junction. She may also do other classes nearer to you that I don't know about. I've done it with both my children. Joanna is lovely and the best teacher (had another on the odd occasion to cover Joanna, but they weren't as good), and my children loved the classes. It was so much fun to sign with them, and they both learnt to talk quickly and with a wide vocab - I'm sure it's because of the signing!